Macro hygiene pass is not aware of const fields structs

[Liozou]

Consider a macro that defines a simple struct:

julia> macro bar()
           Expr(:struct, true, :Bar, Expr(:block, Expr(:(::), :field, :Int)))
       end
@bar (macro with 1 method)

julia> @macroexpand @bar
:(mutable struct Bar
      field::Main.Int
  end)

julia> @bar

julia> Bar(4)
Bar(4)

No problem.

Mark the field as const and the hygiene pass starts believing field is a variable instead of a field:

julia> macro foo()
           Expr(:struct, true, :Foo, Expr(:block, Expr(:const, Expr(:(::), :field, :Int))))
       end
@foo (macro with 1 method)

julia> @macroexpand @foo
:(mutable struct Foo
      const Main.field::Main.Int
  end)

resulting in the confusing error message:

julia> @foo
ERROR: syntax: expected assignment after "const" around REPL[7]:1
Stacktrace:
 [1] top-level scope
   @ REPL[7]:1

Of course a solution consists in wrapping :field in an esc call, but that shouldn't be necessary (since it's not necessary in the first case).